The present invention relates generally to threaded fasteners of any size, and may be useful for threaded fasteners having a major diameter between about 0.8 millimeter and about 6 millimeter.
Threaded fasteners such as screws are used in many applications to connect one component or part to another. Many screws are installed through a portion of one component and threaded into second component to clamp the components together. Many component shapes and configurations have been contemplated for retaining a threaded fastener, such as a blind or through hole formed in the component for engaging the threads of the fastener. The blind or through hole may be provided in an embossment or may be provided in the component material thickness.
Many applications including automotive, electronic, and consumer products require threaded fasteners that maintain desired clamping forces through vibration and other in-use loads. A common problem with prior fasteners included loosening under vibration. Other prior fasteners stripped too easily during installation providing reduced clamping and premature assembly failure. Certain prior fasteners create excessive radial stress around the hole during installation, particularly in an embossment, that weakens the component and may cause premature assembly failure.
Fastener coatings have been developed to compensate for some of the failures of prior fasteners, such as thread-sealing adhesives, thread lubricants, and anti-vibration coatings. However, thread coatings require additional material cost and application cost, and are increasingly difficult to apply as fastener sizes become smaller. There remains a need for a threaded fastener that overcomes these and other disadvantages of the prior art.
We have found that increasing the range of seating torque for installing the fastener, or the seating torque window, reduces strip-out failures by providing for greater variability of the screw driver. Therefore, what is disclosed is a threaded fastener comprising a threaded portion with a ratio of pitch diameter to minor diameter less than 1.28, and the threaded portion with a major diameter portion, a leading flank having a normal angle between 10° and 60°, a trailing flank having a normal angle between 1° and 30°, and a shank portion extending between the trailing flank and the leading flank of adjacent threads of a arcuate surface having a radius greater than the thread height. The ratio between the axial length of the shank portion to thread height may be between 1.5 and 3.0. The arcuate surface forming the shank portion may have a radius between 1.2 and 1.8 times the thread height.
The normal angle of the leading flank of the threaded portion may be greater than the normal angle of the trailing flank of the threaded portion. Alternatively or in addition, the normal angle of the leading flank of the threaded portion may be between 1.5 and 2.5 times the normal angle of the trailing flank of the threaded portion. Alternatively, the normal angle of the leading flank and the normal angle of the trailing flank may be substantially the same. In yet another alternative, the normal angle of the leading flank and the normal angle of the trailing flank may be compound angles.
The threaded fastener may be adapted to assemble parts made from materials of plastic, brass, aluminum, wood, concrete, and steel.
The threaded fastener may include a plurality of grooves extending transversely through the major diameter portion of the threaded portion. Alternatively or in addition, the threaded fastener may include a plurality of grooves extending transversely through the major diameter portion of adjacent threads of the threaded portion.
The major diameter portion of the threaded portion may be tapered toward the leading flank, the trailing flank, or both. Alternatively, the major diameter portion of the threaded portion may be arcuate.
The threaded fastener may have at least one minor protrusion formed along at least a portion of the shank portion of the threaded portions positioned between the trailing flank and the leading flank of adjacent threads. The minor protrusion may be continuous along the shank portion positioned between the trailing flank and the leading flank of adjacent threads. Alternatively, the minor protrusion may be intermittent along at least a portion of the shank portion positioned between the trailing flank and the leading flank of adjacent threads. The height of the minor protrusion may be not more than 30% of the thread height. Alternatively, the height of the minor protrusion may be not more than 20% of the thread height. At least a part of the minor protrusion may have a cross-sectional shape selected from the group consisting of arcuate, rectangular, elliptical, trapezoidal, and triangular. A lead side of the minor protrusion may have a normal angle between 10° and 60°.
Also disclosed is a threaded fastener comprising a threaded portion with a major diameter portion, a leading flank having a normal angle between 1° and 60°, a trailing flank having a normal angle between 1° and 60°, and a shank portion extending between the trailing flank and the leading flank of adjacent threads, and at least one minor protrusion formed along at least a portion of the shank portion of the threaded portions positioned between the trailing flank and the leading flank of adjacent threads.
The minor protrusion may be continuous along the shank portion positioned between the trailing flank and the leading flank of adjacent threads. Alternatively, the minor protrusion may be intermittent along at least a portion of the shank portion positioned between the trailing flank and the leading flank of adjacent threads. The height of the minor protrusion may be not more than 30% of the thread height. Alternatively, the height of the minor protrusion may be not more than 20% of the thread height. At least a part of the minor protrusion may have a cross-sectional shape selected from the group consisting of arcuate, rectangular, elliptical, trapezoidal, and triangular. A lead side of the minor protrusion may have a normal angle between 10° and 60°.
The leading flank of the fastener may have a normal angle between 10° and 60°, and the trailing flank may have a normal angle between 1° and 30°.